The insert and revolve technique: a novel approach for inserting cages during unilateral biportal endoscopic assisted fusion surgery for effective spinal alignment restoration.

Study design: Retrospective study.

Purpose: This study aimed to propose a method of performing unilateral biportal endoscopy (UBE)-assisted interbody cage insertion for fusion using the "insert and revolve" technique and analyze the clinico-radiological outcomes.

Overview of literature: UBE-assisted lumbar interbody fusion (ULIF) is a rapidly evolving technique combining the advantages of minimally invasive technique with ease of learning. The limited size of cages was a result of the narrow insertion channel. We propose a technique in which large extreme lateral interbody fusion cages can be inserted through the same opening.

Methods: This study included 104 patients who underwent ULIF using the "insert and revolve technique" between July 2019 and September 2022. The patients were followed up for at least 12 months postoperatively. The clinical outcomes were assessed using the Visual Analog Scale (VAS) for leg pain and back pain, Oswestry Disability Index (ODI), and modified McNab's criteria. Changes in segmental lordosis (SL), intervertebral disc height (IVDH), segmental coronal alignment (SCA), cage subsidence, and fusion grade were evaluated at 6- and 12-month follow-up.

Results: The VAS scores for leg and back pain and ODI score showed significant improvement. Based on the Macnab's criteria, 97 patients showed excellent outcomes and seven demonstrated good outcomes at 12 months. The mean IVDH increased from 6.3±2 to 10±2.1 mm immediately after surgery and 10±1.1 mm at 6 months. SL improved from 9.3°±11.5° to 17.78°±8.1°, while SCA improved from 7.7°±2.1° to 3.4°±1.2° at 1 year. Moreover, 92 and 11 patients showed grade 1 and 2 fusion, respectively, according to the Bridwell grading at 1 year.

Conclusions: The "insert and revolve technique" facilitates the successful insertion of large cages, contributing to the restoration of disc height and coronal and sagittal spinal correction with favorable fusion rates.